In recent year, researches on an optical coherence tomograph (OCT) which visualizes the depth structure of the inside of a living body using an interference effect of light are being advanced.
In particular, recently, an optical coherence eye-fundus tomography device capable of observing a three-dimensional image of the inside of a retina has been appeared, which works well when diagnosing diseases which may lead to blindness.
Conventionally, a low-coherence interferometer is used as one of such optical coherence eye-fundus tomography devices. As such optical coherence eye-fundus tomography devices, a time domain optical coherence eye-fundus tomography device (Time-Domain OCT (hereinafter, referred to as “TD-OCT”)) is known which visualizes the depth structure of the inside of a living body based on an interfering signal of an object in the depth direction obtained by mechanically manipulating the reference optical path length.
The TD-OCT has a low coherence light source having a wide wavelength width, and split a light beam from the light source into two beams, and irradiates one of the two beams on an object, “an eyeball.”
The TD-OCT scans the object in the depth direction using the one of the two beams (hereinafter, referred to as “object scanning light beam” or “probe light beam”). Further, the TD-OCT performs interference of the object scanning light beam and the other split beam of the two beams, which is a beam for reference (hereinafter, referred to as “reference light beam”). The TD-OCT detects the scattering position of the object based on the interference fringe pattern generated by interference of the object scanning light beam and the reference light beam.
The TD-OCT scans an object by sweeping the object scanning light beam in a cross direction with respect to the optical path of the object scanning light beam, or by moving the object in a cross direction with respect to the optical path, and then, obtains an image of the cross-section of the object (See, for example, Non-Patent Document 1).
On the other hand, a spectrum domain OCT (Fourier Domain OCT (hereinafter, referred to as “FD-OCT”)) which performs interference of light waves on a Fourier space (spectrum domain) not on a real space (time domain), without using such mechanical scanning in the depth direction, is known. The FD-OCT has a measurement speed several tens of times, compared with the TD-OCT.
Similar to the TD-OCT, the FD-OCT calculates the resolution of an object in the depth direction, using two split light beams and a low-coherence interference principle. However, in the FD-OCT a reference light beam and an object scanning light beam which scans an object enter a spectroscope in a parallel, and dispersed simultaneously in the spectroscope to perform interference in a spectrum domain.
The FD-OCT measures a spectral interference fringe generated by the interference by a CCD, and performs a Fourier transform on the spectral interference fringe. As a result, the FD-OCT obtains the reflection distribution of an object in the depth direction.
In particular, the FD-OCT irradiates measure points on a retina forming surface with the object scanning light beam by driving a galvano-mirror in order to obtains a three-dimensional tomographic image. Since the FD-OCT can obtain a three-dimensional tomographic image only by two-dimensional mechanical scanning, a high speed tomographic measurement can be performed (see, for example, Non-Patent Document 1).
In addition to the above-mentioned OCTs, a wavelength sweeping OCT (i.e., swept source OCD (hereinafter, referred to as “SS-OCT”) is also known which makes a spectroscope needless by sweeping the oscillation wavelength of a light source and sweeping the wavelength of the light source (see, for example, Non-Patent Document 1).